Keep track of source name on all allocated SymInts (#90295)
Wow, I had to sweat so much to get this PR out lol.
This PR enforces the invariant that whenever we allocate SymInts as part of fakeification, the SymInt is associated with a Source, and in fact we store the string source name on SymbolWithSourceName. We use 'sname' as the shorthand for source name, as 'name' is already used by sympy to name symbols.
In order to store source names, we have to plumb source names from Dynamo to PyTorch. This made doing this PR a bit bone crushing, because there are many points in the Dynamo codebase where we are improperly converting intermediate tensors into fake tensors, where there is no source (and there cannot be, because it's a frickin' intermediate tensor). I've fixed all of the really awful cases in earlier PRs in the stack. This PR is just plumbing in source names from places where we do have it.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90295
Approved by: https://github.com/voznesenskym
